coding and standard deviation

[royal panther]

(dont have sigma sum symbol on copy paste so im using S instead)
For a set of data, n = 100, S(x-20) = 125, and S(x-20)^2 = 221
a) Find the mean and standard deviation of x
b) Use the fences (mean plus or minus 2 std deviations) to test whether the value x = 19.6 is an outlier

i dont get this at all

<@&791435371564892232>

[unique crane]

not entirely sure but for a isnt the mean just 125/100

[royal panther]

well that is the mean of the coded data set

you would add 20 to that to get a mean on 21.25

[unique crane]

ohh this is to do with coding?

[royal panther]

yeah is ijn title :)

[unique crane]

havent learnt coding proper

[royal panther]

ah

[unique crane]

flip i didnt even see that my bad

[royal panther]

i have test on friday and there are some weird coding questions qwith satandard deviation i dont get

[unique crane]

but wouldnt the standard deviation of the codded data be the same as the original data

the mean wouldnt ofc

[royal panther]

yeah but i dont know how to get the standard deviation of the coded data

[unique crane]

just write the set of numbers

after it has been coded

[royal panther]

that is the full quesstion

there is no lkist of numbenrs

[unique crane]

then do the formula

yh so its root 221/100 - (125/100)^2

is it not??

[royal panther]

one sec

yeah thats right

i still barely get it 💀

i dont get one part

if 221 = x^2

and u want (x-xmean)^2

dont u have to do (root221-1.25)^2

[unique crane]

nah

to be honest i dont know the derivation of the formula

but u can remember it like this

the mean of the squares minus the square of the mean

[unique crane]

root the whole ting btw^^

and the mean is Sfx/n

[royal panther]

formula is root((sum of x - xmean)/n)

[unique crane]

yhh

sum of x^2

divided by n

• the mean

[unique crane]

squared

[unique crane]

ahh i get why u say this

i searched up the formula

[unique crane]

btw for part 2

when u get ur standard deviation

multiply it by 2

[royal panther]

i get part 2

[unique crane]

ohh rigt

calm then

[royal panther]

isnt there 2 different formulas tho

[unique crane]

i dont think so

[royal panther]

left is how im thinking but what u did is on right

[unique crane]

i have never seen or used the one with n-1 on the left

[royal panther]

more like that

oh ignore n-1

[unique crane]

but the one on the left is for a sample

and right is population

[royal panther]

what does that even mean

[unique crane]

population?

its the entirety of the group ur tryna test

[royal panther]

no i know differenc ebetween sample and population but how wld you know in a question like this whether it is sample or population

[unique crane]

ill be real i have never had to use ur formula i always use the one i said

so far it has worked fine

[royal panther]

so the one on the right

[unique crane]

i dont wanna say theres no significance to your one

must be some reasoning

go on pmt

[royal panther]

idk in my textbook

[unique crane]

and do a bunch of questions

and you will hopefully spot a pattern

[unique crane]

what exam board?

[royal panther]

edexcerl

[unique crane]

oh same

ahh

its the same thing

@royal panther

[royal panther]

ok

its confusing bc there first one doesnt work when you sqrt 221

i think its best to just use the one on the right

[unique crane]

yh stick to the second one